A wide variety of band heaters have been designed and manufactured over the years for use in a wide variety of industrial applications, including use on injection molding extrusion nozzles, barrels, blown film dies, and process heating for tanks and plattens, to name a few. Accordingly, band heaters are typically custom fabricated based upon the particular specifications of the end user so that such heaters will be appropriate for the specific application of the end user. Besides specifying the particular performance characteristics and operating factors desired in a particular band heater unit, the end user specifies the degree of expandability of the unit necessary for installation purposes. In this regard, band heaters are typically fabricated so as to be either expandable or non-expandable depending upon how they will be attached to the particular object to be heated. For those applications where the band heater can be easily slipped over one end of the particular cylindrical object to be heated without any hindrance or interference from other objects associated with or attached to the particular object to be heated, a non-expandable band heater may be utilized. On the other hand, expandable band heaters are commonly used where installation of a non-expandable band heater would require the removal of objects or other components prohibiting the sliding of the band heater over the particular object to be heated. Such expandable band heaters may be opened up, or expanded, to allow them to be fitted around the particular cylindrical object to be heated without requiring removal of any of the obstructions. This expansion capability is typically provided by either notching or scoring the metal sheath which encloses the heater elements, or by constructing the metal heater sheath so as to include an expansion seam or joint positioned intermediate the opposite end portions of the heater.
Certain types of expandable band heaters must be constructed as multiple segment heaters in order to protect the insulation material contained therein which would otherwise bridge the expansion seam or joint and be subject to cracking or other damage during expansion. This is particularly true in multi-segment band heaters utilizing layers of organically bound ceramic particles such as aluminum oxide and/or magnesium oxide, or any combinations thereof, as such insulation materials when baked out to cure the same become somewhat inflexible or brittle and are highly susceptible to cracking or other damage when the heater is expanded or spread apart for installation purposes, particularly in the vicinity of the expansion seam. Such cracking and/or other damage to the insulation material at any point within the metal sheath decreases performance and reliability of the band heater since various components of the band heater may have a tendency to loosen, short-out, oxidize during operation, and/or otherwise result in performance problems. Accordingly, such band heaters are manufactured so as to include multiple heater segments, typically, one heater segment on each opposite side of the expansion seam or joint, although any plurality of heater segments can be utilized in any particular band heater construction depending upon the overall diameter or size of such heater. The internal configuration of each heater segment may be constructed in accordance with known constructions such as, for example, those described in U.S. Pat. Nos. 5,359,179 and 4,203,197. Because there is no internal electrical connection across the expansion seam connecting the heating element or resistance wire associated with each heater segment, such prior art constructions require a separate set of termination leads for each separate heater segment housed in a common sheath. This not only increases the overall cost of the heater, but such construction likewise complicates the connection of such heaters to a power source. FIGS. 1 and 2 illustrate examples of such prior art constructions. There is therefore a need for an expandable multi-segment band heater construction which utilizes a reduced number of sets of lead wires or other termination connections in order to provide power to each of the heater segments.